DNA-based monitoring uncovers contrasting salinity-driven diversity patterns of bacterial and protist plankton in the Baltic Sea area.

Salinity influences bacterial community composition more strongly than protists in the Baltic Sea, with bacterial diversity remaining stable despite community shifts across salinity levels.

• Why it matters: Understanding how salinity shapes microbial diversity is crucial for predicting ecosystem responses to environmental changes, yet the contrasting patterns between bacteria and protists are not well understood.
• What they did: DNA metabarcoding was used to analyze protist and bacterial diversity in 398 surface water samples from the Baltic Sea and Kattegat-Skagerrak, focusing on community composition and alpha diversity across the salinity gradient.
• The result: Protist alpha diversity increased with salinity and followed patterns of local adaptation, while bacterial alpha diversity remained similar across salinities despite community turnover, highlighting distinct eco-evolutionary dynamics.